This invention relates to the repair of shatterproof glass laminates of the type used in automobile windshields, and particularly to an apparatus and method for repairing conical cracks or "pock marks" by the use of a chemical repair liquid.
Various devices and methods for repairing windshields by the use of chemical repair liquids are known. When a stone strikes a windshield, it frequently causes a cone-shaped piece of glass to separate from one of the glass laminations, thereby causing a conical crack or pock mark. In general, repair is accomplished by introducing a chemical repair liquid into the space surrounding the separated cone. The liquid polymerizes to form a solid which has an index of refraction very near that of the glass lamination. If the repair is accomplished successfully, the damage becomes very nearly invisible. Glass repair processes using repair liquids are popular because repairing a windshield is much less expensive than replacing it.
Methods of repairing windshields by the use of chemical repair liquids are described in the following U.S. Patents: Forler et al. No. 3,841,932; Sohl No. 3,562,366; Luhmann No. 3,988,400; Werner et al. No. 3,993,520; Story No. 4,132,516; Jacino No. 4,200,478; Petersen No. 4,249,869; Ogden et al. No. 4,165,397; Hollingsworth No. 3,765,975; Miller No. 4,032,272; and McCluskey et al. No. 4,047,863.
The most difficult problem in making a successful repair is the presence of gas bubbles in the repair liquid. These bubbles can be air or other dissolved gases. If they appear in the liquid before it is injected into the crack and are not removed, or if they appear as the liquid polymerizes in the crack, they may remain in the polymer permanently. A few small bubbles in the polymer will result in an unsatisfactory repair.
Werner et al. U.S. Pat. No. 3,993,520 describes a typical method of avoiding gas bubbles. Dissolved gas is removed from the repair liquid within a syringe by turning the syringe so that its needle points up, placing a rubber block over the end of the needle, and withdrawing the plunger to produce a vacuum. Bubbles are allowed to form within the syringe. With the needle still pointed upwardly, the rubber block is removed and the plunger is pushed upwardly to expel gas through the needle.
In accordance with Werner et al., gas is also removed from the liquid while the liquid is in the break in the glass itself. This is accomplished by withdrawing a plunger of a piston and cylinder device used to force liquid into the break.
Various other patents relating to windshield repair are concerned with the removal of gas from the repair liquid while the liquid is located in the conical crack being repaired. These U.S. patents include the Werner et al. patent as well as Hollingsworth No. 3,765,975, Ogden et al. No. 4,165,397, Jacino et al. No. 4,200,478, Petersen No. 4,249,869 and Story No. 4,132,516. While these patents are primarily concerned with removing bubbles from the chemical while it is in the conical crack, some of them disclose apparatus which is also capable of degasing the chemical before it enters the crack.
Miller U.S. Pat. No. 4,032,272 and McCluskey et al. U.S. Pat. No. 4,047,863 describe systems which use continuous vacuum pumps to evacuate enclosures which surround plunger assemblies and hold them in place on the windshield while the repair takes place. The plunger assemblies are used to force repair liquid into the area to be repaired.
The system of the Miller patent uses a vacuum to hold the plunger assembly in place and also to evacuate the crack before the repair liquid is introduced. However, the Miller system does not expose the repair liquid to the vacuum. Consequently, the vacuum in Miller does not effect degasing of the liquid.
In the McCluskey et al. patent, repair liquid is held in a temporarily constructed putty dam on the windshield, and a vacuum is applied to the enclosure surrounding the dam and the area to be repaired. Dissolved gas is removed from the liquid by the vacuum. Following the degasing of the liquid, a plunger assembly is installed in the cup, and is used to force the liquid from the dam into the conical crack.
The McCluskey system is similar to the Miller system in that it makes use of a continuously operating vacuum pump to hold the plunger assembly in place during the repair. It has the advantage over the Miller system that it enables the vacuum produced by the continuously operating pump to be used to degas the liquid before it enters the crack to be repaired. However, in order to accomplish this, it requires a separate dam to hold the liquid.
An improvement over the McCluskey and Miller systems has been developed in Canada by Duan Klettke. The Klettke improvement is described in U.S. Pat. No. 4,385,015, dated May 24, 1983. The Klettke improvement uses a continuous vacuum pump to hold a plunger assembly in place, and uses this same source of vacuum to effect degasing of the repair liquid before it enters the conical crack. It does not require a special dam to hold the liquid while it is being degased.
The present invention is an improvement over the systems of McCluskey and Klettke. Since it will be described as a modification to the Klettke system, it will be important to understand the structure of the Klettke apparatus and the method by which it is used.
The Klettke apparatus uses a vacuum cup similar to the one described in the McCluskey et al. patent. The vacuum cup is provided with a plunger and cylinder assembly for the injection of liquid into a conical crack. The cylinder assembly extends from an end wall of the cup to the opening of the cup, and is there provided with a seal positioned to engage the face of the glass being repaired and isolate the interior of the cup into two separate volumes, one being inside the cylinder, and the other being within the cup but outside the cylinder. The piston is threaded into the cylinder, and is removable so that repair liquid can be introduced into the cylinder. The cylinder itself acts as a dam or reservoir, holding a small quantity of repair liquid against the face of the glass. The piston is in sealing relationship with the interior wall of the cylinder, and is capable of forcing the liquid into the crack as the piston is moved toward the crack. A transverse hole is provided in the cylinder a short distance away from the sealing means at the end of the cylinder. This transverse hole provides fluid communication between the volume within the cylinder and the volume within the cup but outside the cylinder when the piston is retracted.
In operation, the Klettke assembly is placed over the area to be repaired so that the peak of the conical crack is centered underneath the end of the cylinder. Repair liquid is introduced into the opposite end of the cylinder, and the piston is threaded partway into the cylinder, but not so far as to cut off fluid communication through the transverse hole. A vacuum is then drawn on the interior of the cup by a continuous vacuum pump. Because the transverse hole is open, a vacuum is simultaneously drawn on the interior of the cylinder, and the effect of the vacuum is to remove dissolved gas from the repair liquid within the cylinder. The vacuum is allowed to act for a sufficient period of time to alloy all gas bubbles to reach the surface of the repair liquid. The piston is then moved downwardly to cut off fluid communication through the transverse opening in the cylinder and force repair liquid into the conical crack. The vacuum is maintained on the cup at this time to hold the cup, and the piston and cylinder assembly, against the windshield. After the liquid is introduced, the vacuum is released, the repair assembly is removed, and the repair area is finished off and polished in the conventional manner.